In embodiments, the invention provides apparatus for applying an electrical stimulus to a person's leg in timed relationship to leg movement during walking in order to achieve a benefit.
For example, a person who has a dropped foot is unable to lift his or her toes clear of the ground during the swing phase of walking. Such a problem is seen in people who have either a peripheral nerve lesion, as a result of trauma or disease, or an upper motor neuron lesion. It is the latter that responds to neuromuscular stimulation. Lesions of the lower motor neurons result in destruction of the neural pathway so that muscle contraction can be achieved only through direct stimulation of the muscle fibers. Functional electrical stimulation may therefore be suitable for the treatment of patients following stroke, multiple sclerosis, spinal cord injury T-12 and above, Parkinson's disease, cerebral palsy, head injury and familial or hereditary spastic paraparesis.
The first reference to functional electrical stimulation (FES) is the work by Liberson et al, “Functional electrotherapy in stimulation of the peroneal nerve synchronized with the swing phase of gait of hemiplegic patients”, Arch. Phys. Med. Rehabil. 42, 202-205 (1961). At this time electrotherapy was commonplace, but functional electrotherapy was a new concept. Liberson defined it as follows: ‘ . . . to provide the muscles with electrical stimulation so that at the very time of the stimulation the muscle contraction has a functional purpose, either in locomotion or in prehension or in other muscle activity. In other words, functional electrotherapy is a form of replacement therapy in cases where impulses coming from the central nervous system are lacking.’
Liberson used a portable stimulator to correct drop foot during walking A train of pulses of 20-250 μsec duration, frequency 30-100 Hz and maximum peak current 90 mA was applied through conductive rubber electrodes. The negative (active) electrode was placed over the common peroneal nerve below the knee and the large indifferent electrode either on the thigh or on the lower leg. The stimulator was worn in the pocket and a heel switch was used to trigger the stimulus during the swing phase of the gait cycle. The switch was worn within the shoe or on the foot on the affected side so that the electrical circuit was interrupted during the stance phase, when the weight was on the heel, and allowed to flow when the heel was lifted during the swing phase. Liberson was enthusiastic about the results, reporting that all the subjects experienced considerable improvement in gait. Despite improvements in the apparatus used, the basic idea of FES has remained unchanged. Sixteen papers on the topic published in the period 1960-1977 have been reviewed by J. H. Burridge et al, Reviews in Clinical Gerontology, 8, 155-161 (1998).
U.S. Pat. No. 6,507,757 (Swain, the contents of which are incorporated herein by reference) is concerned with improving the reliability of the foot switch. In one aspect it discloses a functional electrical stimulator for attachment to a leg comprising: first and second electrodes for attachment to the leg to apply an electrical stimulus; a foot switch for sensing foot rise or foot strike, said foot switch comprising a force-sensitive resistor; a circuit responsive to said foot switch for generating stimulation pulses; and means forming part of said circuit for responding to changes in the resistance characteristics of said foot switch by adjusting a corresponding response threshold of said circuit.
Various proposals have been made for providing a wireless link between a FES stimulation module and a footswitch. For example, U.S. Pat. No. 7,632,239 (Dar) discloses foot sensor device for gait enhancement comprising a sensor unit having an external casing, said sensor unit being positioned within a shoe of a user and sensing a parameter associated with a gait event An electronic communication unit is electrically associated with said sensor unit, for receiving a signal pertaining to said parameter The electronic unit has (i) a microcontroller, (ii) a transmitting module for transmitting, in a wireless fashion, gait information based on said signal, to a unit of the orthosis external to the foot sensor device, and (iii) a housing for housing at least one of said microcontroller and said transmitting unit. A fastening unit is attached to said housing, said fastening module being adapted to fasten on to said shoe, so as to secure said electronic communication module in a substantially fixed position during gait of said user and including a clamp module for fastening onto a rim of the shoe. In the field of analysing weight shift to different parts of the foot during golf or other sports U.S. Pat. No. 7,758,523 (Collings) discloses an orthotic body including an arch support, a cavity being formed in that support and a wireless transmitter being built into the cavity.